With the diminishing supply of crude oil, the use of renewable energy sources is becoming increasingly important as a feedstock for production of hydrocarbon compounds. Plants and animal biomass are being used to produce liquid and gaseous hydrocarbon compounds. One of the advantages of using biomass is that the CO2 balance is more favourable as compared with the conventional hydrocarbon feedstock.
One of the most commonly used biomass material used is lignocellulosic biomass material. Lignocellulosic biomass materials primarily consist of cellulose, hemicellulose, and lignin bonded together in a complex gel structure along with optional small quantities of extractives, pectins, proteins, and/or ash.
Cellulose and hemicellulose, when hydrolysed into sugars, can be further converted into ethanol and other useful products and intermediates, for example through microbiological fermentation technologies or through thermochemical conversions, such as aqueous phase reforming. In addition hemicellulose present in the lignocellulosic biomass material can be processed to obtain sugars which can later be converted to fuels and chemicals, such as furfurals. Furfural has various applications in the chemical and petrochemical industry and the derivatives of furfural are also useful as polymers and resins.
Various problems associated with the production of the furfural arise due to the complex chemical structure of the lignocellulosic biomass material. The separation of the hemicellulose from other lignocellulosic constituents is complicated by the fact that lignin can be intertwined and linked in various ways with cellulose and hemicellulose. Pretreatment of the lignocellulosic biomass material makes the individual components more accessible for processing, thereby easing the production of furfural from hemicellulose. Existing pretreatment processes, however, have several drawbacks.
The use of organic solvents, such as formic acid and acetic acid, in pretreatment procedures has the disadvantage that solvent recovery is a cumbersome and expensive process step.
The use of steam for destructuring/decomposition of biomass, such as for example by “Steam explosion”, “steam cooking”, “pressure cooking in water”, “dilute acid hydrolysis”, “liquid hot water pretreatment”, and “hydrothermal treatment”, has the disadvantage that they are carried out at higher pressures and may change the properties of lignocellulosic biomass materials. This can result in degradation of sugars and formation of inhibitors.
EP-346836 describes a process and apparatus for continuous preparation of 2-furaldehyde, cellulose and lignin from lignocellulosic material. The described process requires a lignocellulosic material with a reduced particle size in the range from about 2 to about 10 mm. This lignocellulosic material is first swelled at 70 to 90° C., whereafter part of the water is extorted. The remaining suspension of lignocellulosic material in water is hydrolysed in a first hydrolyse step at 115 to 135° C., whereafter again part of the liquid is extorted. Hereafter the remaining suspension of lignocellulosic material in water is hydrolysed in a second hydrolyse step in two stages from 160° C. to 180° C. and 200° C. to 235° C. respectively, whereafter again part of the liquid is extorted. This last liquid also contains 2-furaldehyde. A disadvantage of the process as described in EP-346836 are the many steps and the large amount of volumes, energy and equipment needed.
In organosolv pretreatment processes a lignin-extracting solvent blend is used to extract lignin in high temperature and high pressure digesters. Examples of such organosolv pretreatment processes can be found in WO200686861, WO200751269 US20070259412 and US 2008/0299628. However, the organosolv pretreatments have high capital costs, high energy requirement, problems with solvent recovery and less efficiency.
Accordingly, these pretreatment processes share one or several of the shortcomings which include severe pretreatment conditions, high capital costs, high energy requirement and problems of solvent recovery and less efficiency of the pretreatment.